Precursor to surface melting of Si(111) at high temperature

Abstract

The surface structures of Si(111) in the temperature range between 1220 and 1540 K. in which an additional phase is discovered [Phys. Rev. Lett. 85, 5150 (2000)], have been investigated with rocking curves of reflection high-energy electron diffraction (RHEED). From the analysis using the dynamical RHEED calculation, we found that the thermal vibration of surface atoms shows an anisotropic feature, where the mean-square amplitude of the thermal vibration parallel to the surface is about twice as large as the normal component, and the amplitude is extremely enhanced around 1540 K, just below the surface melting temperature, with an enhancement of the anisotoropy. The anharmonic increase in the thermal vibration of the surface atoms plays an important role in the appearance of the additional phase around 1540 K. This result suggests that this structural phase with a large vibrational amplitude acts as a precursor to the surface melting.